In electric equipment, the transformer plays an important role for power conversion or signal isolation. However, a transformer usually generates drastic and notable current and voltage changes during power transmission process. In order to guarantee safety of the transformer during the power transmission process almost all countries have established very strict safety regulations, such as IEC/UL 60950-1:2000 or the like.
Take IEC/UL 60950-1:2000 for instance, it regulates required insulation conditions of the transformer structure for safety implementation, such as creepage distance, clearance and the like. The creepage distance, in an example of two windings, means the shortest distance of electricity passing through the surface of the transformer winding rack while crossing from one winding to another winding. The minimum creepage distance set in the safety regulations has a corresponding distance limitation according to different transformer implementation environments. To comply with the limitation of creepage distance in the safety regulations, the producer has tried to provide a corresponding structure, such as Taiwan patent Nos. I353613, I390558, M421580 and I338310. At present, most producers adopt a common practice of increasing the distance between the primary side and secondary side of the transformer winding rack to extend the creepage distance. But such a practice also increases the size of the transformer winding rack and makes miniaturization impossible. In addition to the aforesaid practice, Taiwan patent No. I338310 provides a first insulation portion protrusive outside significantly to increase the creepage distance of the transformer winding rack. But the protrusive first insulation portion makes the transformer winding rack implementable only on an upright transformer, but cannot be adaptable for horizontal transformer.